Compressible plunger for hypodermic syringe



June 21, 1960 E. S. V. LAUB COMPRESSIBLE PLUNGER FOR HYPODERMIC SYRINGE Filed Nov. 14. 1958 INVENTOR. Zlwvss 72$: 16 L4 as Ua s te, Far 10 COMPRESSIBLE PLUNGER FOR HYPODERMIC SYRINGE Ernest S. V. Laub, Newport Beach, Calif. (615 Poinsettia St., Corona del Mar, Calif.)

Filed Nov. 14, 1958, Ser. No. 773,861

3 Claims. (Cl. 12S.219)

This invention relates to hypodermic syringes, and more particularly relates to the plungers of such instruments.

In my co-pending application, Serial No. 741,027, now Patent Number 2,907,330, I have described a plunger having certain cavities in the plunger head, which cavities open into a zone which may be termed the neck of the plunger, being between the head and the body of the plunger. The head of the plunger is made of resilient material such as a resilient plastic, and when it is subjected to compression, this material is compressed into said cavities, thus allowing a plunger to have considerable diametrical tolerance with respect to the cylinder with which it is to be used. The described cavities all open rearwardly behind the plunger head and therefor do not become filled with the medicament used in the syringe.

However, such a plunger is difiicult to construct in very small diameters. A tuberculin type syringe, for example, must be very carefully calibrated and has a plunger of long stroke and small diameter. Furthermore, even though all cavities in the head of a plunger open rearwardly behind the head and therefor do not become traps for medicaments, they may become traps for contamination if they open to the atmosphere, and therefor such openings should be avoided if possible.

It is an object of my invention to provide a plunger which is compressible and which need not be fitted precisely to the cylinder with which it is matched.

A further object of my instant invention is to provide a plunger having totally enclosed cavities in its head, which cavities permit the plunger head to compress resiliently, the air or other gas within the cavities compressing also and adding to the resiliency.

Still another object of my invention is to provide a plastic hollow plunger reinforced by an internal cylindrical liner of metal or other hard material, the liner providing a conduit leading to a reservoir for the compressed gases.

In the accompanying drawing, illustrative of but not intended as limiting my invention,

Fig. 1 is a longitudinal sectional view of my improved plunger, shown partly inserted in a cylinder;

Fig. 2 is a transverse sectional view on the line 2-2 of Fig. l;

Fig. 3 is a transverse sectional view on the line 3-3 of Fig. 1;

Fig. 4 is a longitudinal sectional view of a modified form of plunger;

Fig. 5 is a transverse sectional view on the line 55 of Fig. 4; and

Fig. 6 is a transverse sectional view on the line 6-6 of Fig. 4.

Having reference now to the details of the, drawing, a plunger 10 is shown partly inserted in a cylinder 11. The cylinder 11 has an open end 12 surrounded by a flange 13 to provide a finger-hold for insertion of the plunger, and has a closed end 14 holding a hollow needle 15. The cylinder 11 is preferably made of plastic, molded to as 2,941,530 Pa tented June 21,

,2 g I close tolerances as may be found economical, but with no eifort to attain the extreme tolerances necessary for a glass cylinder which is to receive a glass or metal plunger. The needle 15 has an enlarged end 16 which may be cast intothe plastic material er the closed end 14 when the latter is molded and which then will hold the needle 15 firmly in place. I p

The plunger 10 is, the form shown in Figs. ,1-3, preferably of two-piece construction for simplicity in manufacture, and comprises a head-portion 20 which is integral with a neck portion 21, the head and neck being joined to a base 22. The head 20 has a cylindrical wall 23 containing a cavity 24, and is of resilient plastic material capable of being compressed radially inwardly, the displacement of material being absorbed by the cavity 24. The head 20 is molded to be very slightly over-size for the cylinder 11 into which it is designed to fit, but may have some tolerance in its diametrical proportions, like the cylinder 11, as its resilience will permit it to be compressed to a diameter at which it will enter the cylinder. The neck 21 is preferably reduced in diameter to a little less than the diameter of the head 20, to permit it to slide easily within a cylinder, even when the head 20 has been compressed. However, the cavity 24 in the head 20 is continued in a cavity 25 extending longitudinally of the neck 21, so that the walls of the neck 21 are also responsive to variations of outward and inward pressure to move radially.

The neck 21 is aflixed to a boss 26 on the base 22 by any suitable method, such as by plastic adhesives or by threads, and the cavity 25 may be extended by a passage 27 in the boss 26 which admits to a chamber 28 formed in the base 22. As the base 22 is also preferably of plastic, it may be constructed so that its end wall 29 has a certain amount of flexibility and diaphragmatic action, whereby when pressure is exerted on the wall 29 to force the plunger 10 into the cylinder 11, the pressure is pneumatically conveyed to the walls of the head 20 and of the neck 21, to ensure a leak-proof contact with the cylinder 11.

In Figs. 4-6, I have shown a modification of my plunger which is suitable for a tuberculin syringe of high calibration. A plunger for this purpose is longer and thinner than that found in the usual hypodermic syringe, and if made of plastic, and particularly of plastic having some degree of flexibility and resiliency, it may not have the rigidity necessary to enable it to be forced into a syringe. Accordingly the plunger '30 has a resilient plastic head 31 with a cylindrical wall 32 containing a cavity 33. Integral with the head '31 is a long, narrow neck 34 which attaches in the manner hereinbefore described to a boss 35 on a base 36. The neck 34 has a central cavity 37 communicating between the cavity 33 in the head 31 and a chamber 38 in the base 36. A tube 39 of metal or other hard and non-flexible material lines the cavity 37 and gives rigidity to the neck 34. The flexible end wall 40 of the base 36 gives a limited oil-can action. It will be obvious that pressure may be transferred pneumatically between the cavity 33 and the chamber 38 without, in the case of this modification, distending the neck 34, which will remain rigid and of constant diameter.

The disclosed embodiments are not to be construed as limitations upon my invention, the scope of which is deemed to include any desirable constructive modification within the spirit and breadth of the appended claims.

I claim:

1. In a syringe, including a cylinder: a plunger having a head of resilient material of sufiiciently larger diameter than the internal diameter of said cylinder to necessitate compression of said head in order to insert said head in said cylinder, and having a neck of less diameter than said head disposed adjacent said head, said head having 2,-94-1,sao

a cylindrical wall and having 'a cavity within said wall extending through said neck to receive radial 'inwar'a compression, both ends of said cavity being closed to the atmosphere, said ,plunger .having a base one-the .end of said plunger opposite to sailfh'ead, said .b'ase'binghdllow 5 responsive to variations of ontwardandinward pressure.

In a syringe, the structure set forth in claim 1, in which's'aidn'ekhas a reinforcing liner of hard material encompassing that part of said cavity disposed within said neck.

References Cited in the file of this patent UNITED STATES "PATENTS 2,512,568 Safiir June 20, 1950 2,695,612 Fields Nov. 30, 1954 2,735,735 Abel Feb. 21, 1956 2,831,483 lDeLoren'ze Apr. 22, 1958 

